1. Field of the Invention
This invention relates to the field of wireless communication systems, and more particularly to the field of detecting interference in wireless communication channels.
2. Description of Related Art
As is well known in the wireless data communications arts, a common trade-off in the design of communication systems is performance versus bandwidth. That is, various aspects of communication performance can be improved at the expense of increased radio frequency (RF) bandwidth. One very important factor contributing to the performance of a communication system is the “quality” of the data channels used by the system. As is well known, data reception errors can be caused by the introduction of noise and interference during data transmissions across a channel. Signal interference distorts signals and their associated data during transmissions over the channel. Sources of such noise and interference comprise radio-frequency interference (RFI) including multi-path fading, multiple-access interference and hostile jamming. Channel quality depends largely on the amount of noise and interference that exists on a channel relative to the strength of the signal levels of the channel. A channel that has a small amount of noise relative to the strength of the signals is a high channel quality. Conversely, a channel that has a large amount of noise relative to the signal levels is a low channel quality. Channel quality is typically measured in terms of the signal-to-noise (SNR) or Es/No (i.e., ratio of signal energy to noise energy) of a channel.
A wireless communication system can be properly designed to reliably operate in the presence of various types of noise and radio-frequency interference. For example, signals with very large RF bandwidths can be generated using a well-known method known as adaptive frequency hopping (AFH) in which the carrier frequency of a digital communication signal is adaptively changed, or “hopped”, over a wide range of frequencies. One such AFH digital communication system is the Bluetooth™ protocol system that facilitates the transport of data between Bluetooth™ devices. As described in more detail in the above-incorporated related applications, Bluetooth™ communication systems use a frequency-hopping spread spectrum (FHSS) scheme when communicating between master and slave devices. In accordance with this frequency hopping spread spectrum scheme, frequencies are switched during data transmissions. Frequency hopping is performed in accordance with specified frequency-hopping algorithms so that devices can independently determine the correct frequency-hopping sequences (i.e., ordered lists of frequencies, also sometimes referred to as “hop-sets”). In one example, pseudo-random FH sequences are independently determined by slave devices using their associated master device address and clock information.
Although the FH sequences associated with each Bluetooth™ master device is unique, piconets operating within close proximity can interfere with one another due to the relatively small number of independent channels used by the Bluetooth™ devices. In addition, channel noise and interference can be caused by a number of non-Bluetooth™ devices operating within close proximity to the Bluetooth™ devices. For example, as described in the above-incorporated related applications, an 802.11 protocol device operating within close proximity to a Bluetooth™ device can cause undesirable RF interference rendering one or more of the channels in the Bluetooth device's hop-set unusable.
The FHSS scheme reduces collisions between nearby Bluetooth™ piconets due to the pseudo-random nature of the FH sequence used by the devices. As described in Part B, “Baseband Specification,” Section 11, of the Bluetooth™ Specification, Bluetooth™ communication protocols use a Bluetooth™ FH kernel to select FH sequences and map FH sequences to hop frequencies. Disadvantageously, the Bluetooth™ FH kernel selects hopping frequencies without regard to channel conditions, and thus, a hopping frequency having bad channel conditions (e.g., exhibiting small signal-to-noise ratios) caused by non-Bluetooth™ (FH) interferers can be selected. As is well known, transmitting data on frequencies with bad channel conditions increases the probability of the occurrence of reception errors. In any data communication system, it is desirable to reduce the occurrence of reception errors.
Therefore, a need exists for a method and apparatus that estimates and detects the presence of RF interference on a data channel. The data channel may have been previously determined by an AFH scheme to be “disallowed” (i.e., exhibited bad channel conditions), or it may be a channel within a frequency hop-set. The interference detection apparatus and method should be amenable for use in any communication system where the presence of intermittent interference needs to be detected. The present invention provides such a method and apparatus.